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“As Ukip is to the Tories, so can the Green party be to the Lib Dems.” That’s a sentence I wrote here, almost seven years ago, on 3rd November, 2007.

In The Times, Sam Coates has looked at how the quiet rise of the Greens in recent months – the party polled just ahead of the Lib Dems in May’s European elections – might hurt the Lib Dems at the May 2015 general election.

An analysis of the European election results shows the Green vote strengthening and consolidating in the southwest and parts of Scotland while Lib Dem votes drain away. Demographic groups who once supported Mr Clegg’s party are becoming more favourable to the Greens. The analysis suggests that Lib Dem support is weakening among the young, old, urban, rural, poor, middle class and wealthy, and Greens are advancing in these categories, particularly among 18 to 24-year-olds.

Senior Lib Dems acknowledge that the Greens’ policy platform — which embraces higher public spending, opposes nuclear power and fracking, and pledges to scrap tuition fees — bears a strong resemblance to the Lib Dem manifesto of 2005. The Lib Dems have meanwhile switched positions on these symbolic, easily understood issues. They are also likely to lose their status as the protest-vote party for centre-left voters because of the coalition.

While there is little chance of the Greens taking any additional seats beyond their existing one, there are fears of a Ukip-style effect where they take enough votes from the Lib Dems to hand the seat to the challenger — often the Conservatives in the southwest. One senior Lib Dem said that the party was taking the Greens “not terribly” seriously but added: “Even the loss of 1 per cent or 2 per cent in a marginal seat can be costly.”

Five of the Lib Dems’ ten most marginal seats are in the southwest. They played down the threat, saying that the grassroots organisation of the Greens was “pretty feeble”. A source said: “We must have a clear green appeal in 2015 but not fret about the Green Party.”

The paper quotes Ian Warren, a political analyst and author of the @election-data blog, commenting: “In the southwest the Lib Dems are the effective opposition to the Conservatives and, come the general election I suspect many of the 2014 Greens will revert to type and go Lib Dem. However, many of them won’t, and how they break will determine the outcome. The Greens and Ukip provide a space on the ballot paper for these disaffected Lib Dems.”

I think the Lib Dems have made the right decisions in government — taking a scientific and cautious approach to fracking, recognising new-build nuclear power is a necessary and cleaner part of our energy mix — but there’s no doubt this pragmatism has hurt us with those who want to ban fracking and no more nuclear power. The party is right neither to over-estimate the Greens’ national appeal at general elections, nor to dismiss the threat. Marginal constituencies, by their very nature, are decided at the margins.